Elliptically or circularly polarized antenna



May 7, 1968 M. L. FEE 3,382,501

ELLIPTICALLY OR CI RCULARLY POLARIZED ANTENNA Filed Sept. 22, 1965 Mum/r46 WAUi/CZL F55,

United States Patent O 3,382,501 ELLIPTICALLY 0R CIRCULARLY POLARIZED ANTENNA Maurice L. Fee, Lakewood, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware 7 Filed Sept. 22, 1965, Ser. No. 489,222 7 Claims. (Cl. 343-728) This invention relates to high-frequency antennas and more specifically to antennas capable of radiating and receiving elliptically and circularly polarized wave energy.

In some applications, such as space communications systems, it is desirable to utilize antennas which radiate and receive elliptically or circularly polarized electromagnetic wave energy. The desirability of such antennas stems from the fact that with linearly polarized waves accurate coplanar polarization of the receiving and transmitting antennas is required for optimum transmission. Quite often it is difficult, if not impossible, to accurately maintain such polarization alignment. Circularly polarized antennas are therefore desirable since they obviate the necessity of polarization alignment between antennas.

It is a general object of the present invention, therefore, to provide improved antenna devices for radiating and receiving circularly and elliptically polarized electromagnetic wave energy.

In the past, circularly polarized high-frequency antennas have generally utilized a basic radiating element comprising a form of aperture in a waveguide wall. Apertures in the form of circular holes or crossed slots cut into the broad wall of a rectangular waveguide at a proper location will yield circular polarization. See, for example, the article, Circularly Polarized Slot Radiators, by A. J. Simmons, IRE Transactions on Antennas and Propagation, vol. AP-5, No. 1, January 1957, at page 31, et seq.

In his copending application, 'Ser. No. 489,223, filed Sept. 22, 1965, applicant has disclosed several embodiments of a circularly or elliptically polarized antenna which overcome many of the disadvantages attendant prior art arrangements. Specifically, one of the disadvantages of prior art circularly or elliptically polarized antennas is the decreased antenna efliciency brought about by dissipative load impedances which terminate the waveguide containing the slot radiating elements. In applican-ts above-mentioned copending application this disadvantage is overcome by utilizing an antenna structure capable of standing-wave operation, which has no dissipative load impedance.

The antenna of the present invention achieves increased efi'iciency with an alternative fundamental radiating element. In accordance with the present invention, an openended section of conductively bounded waveguide in combination with a conductive loop attached across the open end thereof comprises the basic radiating element. When operated in its transmitting mode the electromagnetic wave energy from the transmitter is propagated through the waveguide and is radiated at its open end. The electric vector of the wave energy radiated from the openended guide is polarized in a plane determined by the wave mode of the energy within the guide. The wall currents in the waveguide also excite the conductive loop which causes it to radiate. By virtue of the geometry of the loop the phase centers of the two radiated waves are different. Specifically, the phase center of the energy radiated from the open-ended waveguide is in the plane of the open end, whereas the phase center of the energy radiated from the loop is a fraction of a wavelength away from the end of the guide. Elliptically polarized wave energy is thereby radiated from the combined radiating element. By selecting the proper length, shape and connection points of the loop, circular polarization is obtained.

In order that the present invention may be clearly understood and readily carried into effect, it will now be described with reference to the accompanying drawing in which:

FIG. 1 is a pictorial view of a basic radiating element in accordance with the present invention, and

FIG. 2 is a pictorial view of a planar array antenna in accordance with the present invention.

Referring more specifically to the drawings, in FIG. 1 there is shown a pictorial view of a conductively bounded rectangular waveguide 10. One end 11 of waveguide section 10 is adapted for connection to a source 12 of electromagnetic wave ener y. T he other end 13 of waveguide section 10 is open. A loop 14 of conductive wire is mechanically and electrically connected across the open end 13 from one broad wall of guide 10 to the other. Advantageously, loop 14 is bent or twisted so that at least a substantial portion of the loop lies in a plane parallel to the broad walls of waveguide section 10. Each end of loop 14 is soldered, brazed, welded or otherwise secured in position at the end region of the broad walls of waveguide section 10. The distance a between the region of attachment of the ends of loop 14 to the nearest narrow wall of waveguide section 10 and the axial distance 11 from the loop to the open end of the guide can be selected to produce the desired radiation pattern. The perimeter of loop 14 can conform to a substantially rectangular shape, as shown, or can be oval or elliptical as desired. By the same token, the cross sectional geometry of the wire utilized to form loop 14 can be circular, as shown, or can be of any other shape, such as square or rectangular.

It is understood that the embodiment of FIG. 1 can be used as an antenna for either transmitting or receiving electromagnetic Wave energy. As is generally known, the antenna can be connected to a switching device for directing outgoing wave energy from a source such as a transmitter to the antenna, or for directing incoming wave energy from the antenna to a receiver or other utilization device.

The operation of the basic radiating element of FIG. 1 will now be explained in terms of its transmitting mode. Electromagnetic wave energy, which for example can comprise a modulated carrier, is coupled from source 12 to end 11 of waveguide section 10. This wave energy is then propagated through waveguide section 10 toward open end 13 in the dominant TE mode. Upon reaching open end 13 a portion of this wave energy is radiated into space. The phase center of the wave energy thus radiated lies in the plane containing the open end of waveguide section 10. The electric vector of this radiated wave is oriented in a plane perpendicular to the broad walls of the guide as shown by the double headed arrow designated E The wave energy propagating within waveguide section 10 also gives rise to currents which flow in the walls of the guide. These wall currents, together with the wave energy radiated from the open end 13 of the guide, induce an alternating current in loop 14.

By virtue of the current thereby induced, wave energy is also radiated from loop 14. Due to the orientation of the loop, the electric vector of thi radiated energy, however, is polarized in a direction parallel to the broad walls of guide as indicated by the doubleheaded arrow designated E By way of explanation, when there is a combination of two uniform plane waves of the same frequency but having ditferent phases, magnitudes and orientations of the electric field vectors, theresultant combination is said to be an elliptically polarized wave. If two orthogonal waves combine so that the two electric field vectors are 90 out of phase and the magnitudes are equal, then the resultant wave is said to be circularly polarized.

It is therefore seen that the wave energy radiated from the basic radiating element of FIG. 1 is elliptically polarized. Furthermore,.by proportioningloop 14 so that .the phase center of the energy radiated from it is 90 electrical degrees removed from the plane of the open end of waveguide section 10, circularly polarized radiation can be obtained..For circularly polarized radiation, however, the magnitudes of the two electric vectors must be equal. This is achieved by selecting the proper loop length and by properly positioning the ends of the loop along the longer sidesof Waveguide section 10 at open end 13. i

It should also be noted that the sense (that is, righthand or left-hand rotation) of the resultant electric vector can be changed. This is accomplished by merely connecting the ends of loop 14 between the broad walls at regions near the upper-left corner and the lower-right corner rather than the upper-right corner and lower-left corner as shown.

.By way of example, a basic radiating element similar to that of FIG. 1 was constructed and operated at a frequency of 9160 megacycles per second. For this device, half-height X- band waveguide having internal dimensions of 0.9 in. x 0.2 in. was employed. The wall thickness of the guide was 0.050 in. The axial distance b between the loop and the open end of the guide was 0.375 in. and theends of the loop were attached a distance a equal to 0.20 in. from the narrow walls of the guide.

In FIG. 2 there is shown a pictorial view of a twodimensional or planar array antenna in accordance with the teachings of the present invention. The antenna array of FIG. 2 comprises a plurality of radiating elements consisting of open-ended waveguide sections 21, across which are connected loops of conductive Wire 22 in the manner of the embodiment of FIG. 1. As shown, the antenna of FIG. 2 utilizes nine basic radiating elements which are suitably disposed in a 3 x 3 matrix. The

geometric arrangement and number of individual radiating elements is well-known to those skilled in the art. In general, an antenna array contemplated by this invention can comprise any number of individual radiating elementsthe number of eachdepending upon the radiation pattern desired. v i

In any event,.feed means for applying or extracting wave energy trom antenna array 20 can be provided by a section of primary feed waveguide 24 to which are coupled sections of secondary feed waveguide 25. Each of open-ended waveguide sections 21 are in turn coupled to secondary feed Waveguide sections 25 by suitable coupling means wellknown in the art. If desired, one or more phase shifting devices can be employed to vary the relative phase of the energy radiated from the individual elements.

In all cases it is understood that the above-described arrangements are illustrative of but a small number of many possible specific embodiments which can represent applications of the principles of the present invention. Numerous and varied other arrangements can be readily devised in accordance with these principles by those I skilled in the art without departing from the spirit and having at least one open end, said section being.

capable of supporting propagating electromagnetic wave energy having an electric vector oriented in a given plane of polarization; a thin elongated conductive member in the shape of a loop; and 1 means for conductively connecting each end of said conductive member to opposite sides of said waveguide across said open end, at least a substantial portion of said member being disposed in a plane substantially perpendicular to said given plane. 2. In combination, a section of hollow conductively bounded rectangular waveguide having at least one open end; a thin elongated conductive member in the form of a loop; and means for conductively connecting each end of said conductive member to opposite broad walls of said waveguide across said open end, at least a substantial portion of said loop being disposed in a plane sub stantially parallel to said broad walls. 3. A high-frequency antenna comprising, in combination,

a section of hollow conductively bounded waveguide supportive of propagating electromagnetic wave energy in the TE mode; and a loop of conductive wire, each end of said loop being conductively connected to one of the broad walls of said waveguide across said open end.

4. A high-frequency antenna comprising, in combina" conductively bounded waveguide, .each of said waveguide sections having at least one open end;

a plurality of thin elongated conductive members in the form of loops; and

means for conductively connecting respective ends of each of said conductive members to opposite sides of each of said waveguide sections across said open ends.

6. A high-frequency antenna comprising, in combination,

a plurality of substantially identical sections of hollow conductively bounded rectangular waveguide contiguously disposed in a planar array; and

a plurality of loops of conductive wire, respective ends of each of said loops being conductively connected to respective broad walls of said of said waveguide sections across said open ends, at least a substantial portion of each of said loops being disposed in a plane substantially parallel to said broad Walls.

7. In an antenna of the class comprising a plurality of sections of open-ended rectangular waveguide arranged in an array, means for obtaining elliptical polarization in such an array, said means comprising a loop of conductive wire conductively connected across each of said open ends, respective ends of each of said loops being connected to respective broad walls of each of said wave guide sections and at least a substantial portion of each 5 6 of said loops being disposed in a plane substantially pal-211* 2,972,147 2/ 1961 Wilkinson 343-756 X lel to said broad walls. 3,164,834 1/1965 Nikolayuk 343-771 References Cited HERMAN KARL SAALBACH, Primary Examiner. UNITED STATES PATENTS 5 ELI LIEBERMAN, Examiner. 2,663,797 12/1953 Kock 343-786 R. F, HUNT, S. CHATMON, 1a., Assistant Examiners.

2,946,055 7/1960 Faflick 343756 X 

1. IN COMBINATION, A SECTION OF HOLLOW CONDUCTIVELY BOUNDED WAVEGUIDE HAVING AT LEAST ONE OPEN END, SAID SECTION BEING CAPABLE OF SUPPORTING PROPAGATING ELECTROMAGNETIC WAVE ENERGY HAVING AN ELECTRIC VECTOR ORIENTED IN A GIVEN PLANE OF POLARIZATION; A THIN ELONGATED CONDUCTIVE MEMBER IN THE SHAPE OF A LOOP; AND MEANS FOR CONDUCTIVELY CONNECTING EACH END OF SAID CONDUCTIVE MEMBER TO OPPOSITE SIDES OF SAID WAVEGUIDE ACROSS SAID OPEN END, AT LEAST A SUBSTANTIAL PORTION OF SAID MEMBER BEING DISPOSED IN A PLANE SUBSTANTIALLY PERPENDICULAR TO SAID GIVEN PLANE. 